Solid state, and quasi solid state, carbon composite electrodes have been known and implemented as far back as 57 years ago. The initial work often utilized a wax material, epoxy, or plastics like poly(methylmethacrylate), Teflon, polyethylene. Some of the advantages of working with a solid state composite electrode are a sandable surface, which can be repeatedly regenerated, acid or base compatibility, tunable solvent compatibility, facile catalyst incorporation, a chemically tunable substrate, geometrical electrode patterning, and a low cost and disposable platform.
Current commercial disposable electrodes are typically produced with automatic screen printers and are simply referred to as screen printed electrodes (SPEs). An automatic screen printer cost >10,000 dollars and requires a skilled operator. The resulting SPE are typically incompatible with popular organic solvents used in electrochemistry. SPEs generally have a lower electrochemical activity and have high cell resistances of 100's of Ohms. In a sensor, low activity of SPE can cause problems with multiple analyte detection (poor resolution), as well as detection limits. Higher cell resistances make SPEs a poor choice for kinetic measurements, limiting their use in fundamental electrochemical research. Studying electrochemical kinetics is critical in understanding the underlying mechanisms/chemistry in the fundamental research of sensors, as well as electrochemical energy storage and/or generation. Lastly, SPE are typically crudely coupled with complex electrochemical systems such as microfluidics because they are not directly integrated into the microfluidic substrate. Arduous integration of SPE into complicated electrochemical systems hinders the development of carbon electrode integration into the so called “lab on a chip”, a revolutionizing analytical sensing technology.
Initial attempts with PMMA and graphitic composite carbon electrodes utilized an elaborate radiation-based method to fabricate electrochemical electrodes. Later, a spray coating technique was developed involving PMMA and graphite dissolved in butyl acetate to fabricate electrodes for measuring cadmium ions. More recently, Yao and coworkers developed an in-situ polymerization technique for making composite carbon nanotube PMMA electrochemical devices. The process was also adopted by Dia and Zheng from the Guonon Chen laboratory which implements graphitic carbon with PMMA. Additionally, an impregnation technique was proposed to fabricate PMMA:Graphitic electrodes coupled with electrophoresis.
Composite carbon electrodes have been employed in a wide variety of applications, ranging from batteries and fuel cells to chemical sensors, because they are easy to make and pattern at millimeter scales. Despite their widespread use, traditional carbon composite electrodes have substandard electrochemistry relative to metallic and glassy carbon electrodes. As a result, there is a critical need for new composite carbon electrodes that are highly electrochemically active, have universal and easy fabrication into complex geometries, are highly conductive, and are low cost.